Various power applications require reliable battery operation and accurate monitoring during operation. For example, an Uninterruptible Power Supply (UPS) provides back-up power to a load, such as a computing or telecommunications device, when a primary power source has stopped providing power (e.g., due to failure). Accurate monitoring of the UPS battery charge state allows the user to suitably save information and shutdown the device prior to the UPS battery reaching end-of-discharge conditions. As another example, an electric vehicle battery provides power to propel the vehicle. Accurate monitoring of the vehicle battery discharge state provides an indication to an operator of the electric vehicle of how long they can drive the electric vehicle before stopping to prevent over discharge damage to the vehicle battery.
In recent approaches, a battery system is monitored by continuously tracking data from multiple sensors, and comparing this data to stored data accumulated from the battery on its initial discharge cycle, or to a theoretically-based model of the battery's estimated discharge capacity as a function of use or cycles, and then applying a calculation sequence to determine the state-of-charge of the battery. Due to the use of complicated sensors and calculations, including the storing and use of accumulated data over the life of the battery or over one or more discharge cycles, such systems can prove costly and cumbersome. Further, this type of system requires the use of multiple sensors to collect data, a means to accumulate the data and extrapolate or determine state-of-life of the battery (remaining life of the battery in regards to remaining cycles, usable charge, etc.), and may nonetheless terminate discharge too early due to false reads from the sensors caused by: age of the battery or of any one cell in a battery having one or more cells or units; variation in individual battery manufacture; use of mixed battery chemistry that generates a false termination indicator as one reactant is depleted and a second continues to be viable; detection limits of the sensors; or the like. Further, due to these same parameters, the data may generate a false indicator of remaining life, causing the battery to undergo over-discharge, and potentially damaging the battery. In either instance, the status determination of the state of life and/or health of the battery is potentially inaccurate, resulting in the under usage or over usage of the battery, which in the latter instance can lead to permanent damage and the need to replace the battery.
Therefore, it would be desirable to have a system and method for determining state-of-charge, -life, and/or -health of a battery that is determined independent of those parameters that can cause false readings in known methods and systems, and which can make such systems cumbersome and costly to operate and maintain.